BY JAWES NELSON GOWANLOCH 129 



The effect of lowered salinities in causing the migration 

 or death of the parasites was observed by exposing heavily 

 infected, adult Fundulus to a series of different media constituted 

 as follows: (1) Normal sea water with a salinity of approxi- 

 mately 30 parts per mille; (2) Sea-water diluted to a salinity 

 of 20; (3) Sea-water diluted to a salinity of 15; (4) Sea- 

 water diluted to a salinity of 10; (5) Fresh water; (6) Dis- 

 tilled water. In each case the water was thoroughly aerated 

 before use and Fundnlus each bearing from 250 to 500 parasites 

 were subjected to these conditions. It was found that within 

 a half an hour all of the trematodes in distilled water and the 

 majority in fresh water had eitlier left their hosts or were dead 

 but in the salinity of as low as ten parts per mille the Gyro- 

 dactylus remained attached to the host after seventy-two hours 

 exposure. In higher salinities they appeared to carry on their 

 normal activities. The host fish, usually hardy and unaffected 

 by wide variations in salinity, appeared to suffer from diffuse 

 haemorrhages over the surface of the fins when exposed to 

 distilled or to tap water. However the trematodes were affect- 

 ed long before such results appeared in the hosts and as indicated 

 an exposure of less than an hour in distilled water or of less than 

 two hours in fresh water served to completely clear the host 

 fish of trematodes. 



Further observations of the effect of lowered salinities 

 upon the activities and viability of Gyrodactylus were then 

 carried out by the isolation of quantities of the trematodes in 

 watch glasses containing either fresh water or distilled water, 

 the accompanying controls of corresponding numbers being 

 placed in normal sea-water. Without exception these control 

 animals exhibited a normal behaviour throughout the entire 

 course of the experiment. The results may be stated briefly. 

 The trematodes subjected to the action of fresh water showed 

 immediate and extreme distress. Within seven minutes many 

 of the parasites had ceased movement and within fifteen minutes 

 many were dead. In two and a quarter hours two-thirds were 

 dead while at five hours all except two individuals had suc- 

 cumbed. These two exhibited feeble movements and survived 



